The present invention relates to a cylindrical direct current motor. The motor may be provided with speed and/or torque control which can be reversed without changing power connections to the motor. Direct application for the motor is found in driving an electric car; additionally, it may be useful for driving elevators, milling machines and lathes, where infinitely variable speed and torque control and low speed-high torque characteristics are desirable.
There are many different motor structures shown in the prior art. Most of these motors involve inner rotors and require brushes, slip rings and the like. These prior art motors are not pertinent to the present case. A more pertinent motor is disclosed in U.S. Pat. No. 3,806,744 (Abraham et al). The Abraham motor involves an inner stator assembly, comprising a series of cylindrically arranged and sequentially energized stator rings, and an outer rotor, comprising a rotatable non-magnetic housing having rows of longitudinally extending magnetic inserts. Each stator ring is briefly energized to draw to it an adjacent magnetic insert. This procedure is repeated from stator ring to stator ring and thus the rotor is caused to rotate.
It will be noted that the Abraham motor involves stator rings which are energized by shared toroidal coils, magnetic inserts which are axially staggered in the rotor, and there is one more stator ring than the number of phases. These features have a substantial influence on the way the motor operates and on its characteristics. It is also noted that only half the stator poles of a ring actually react with rotor inserts at any given time since there are twice as many stator pole pairs per ring as there are rotor inserts.